1. Field of the Invention
The present invention relates to control panels, and more particularly, to control panels with switch keypads.
2. Description of Related Art
Many devices are provided with control panels to allow a user to input information or control the operation of the device. Control panels typically have a keypad with one or more mechanical keys, or switches, which can be selectively actuated. Actuation of a switch generally completes, or breaks, an electrical circuit to thereby provide a signal to the device.
In use, such control panels are often exposed to dirt, moisture, and the like. If these materials are allowed to enter the control panel, the control panel may be seriously damaged. For example, dirt can build up around a switch causing it to jam or stick. Similarly moisture can short circuit the electrical connections within the control panel. In either case, the control panel may fail to function properly. Thus, it is desirable to prevent the entry of moisture, dirt, or other harmful materials into the control panel.
Furthermore, many control panels, such as those used for medical or dental instruments, must be maintained in a clean and sanitary condition. Such control panels must be able to withstand the solvents and disinfectants used to clean them. Moreover, such control panels must preferably be free of cracks, crevices, or corners where dirt can collect and bacteria can multiply.
Many control panels incorporate keypads having one or more membrane switches. There are a wide variety of different types of membrane switches. However, a typical membrane switch has a continuous membrane outer covering. One or more switch locations are embossed or printed on the outer covering. At each switch location an electrical contact is positioned on the underside of the outer covering. A spacer and a substrate are positioned beneath the outer covering. The spacer, which serves to separate the outer covering from the substrate, has an aperture at each switch location. In this manner, when a user presses on a switch location, the outer covering deforms allowing the electrical contact on its underside to be brought into contact with a corresponding electrical contact provided on the substrate. This completes an electrical circuit to provide the appropriate signal to the device.
The outer covering, or membrane, is typically made of plastic or the like and is a single continuous sheet. As a result, it is well suited to prevent the entry of moisture and dirt around the switches. Moreover, the outer covering is typically generally smooth and has no cracks and crevices around the switches to collect dirt and bacteria.
However, the edges of a membrane switch keypad are typically of a layered construction. The outer covering forms a layer, the spacer forms a layer, and the substrate forms a layer. When the edges of a membrane switch keypad are exposed to moisture, the moisture can enter and travel between the layers to the electrical contacts. Similarly, dirt and bacteria can become trapped around the edge of the keypad and work in between or under the layers of the keypad where it can collect and multiply. These problems are exacerbated over time as the adhesive between the layers may degrade and constant use may cause the edges of the membrane switch to delaminate.
In an attempt to overcome these problems, many control panels are constructed with a frame-like member over the perimeter of the membrane switch keypad. In this configuration, the edges of the membrane switch keypad are secured beneath the frame and are not directly exposed to wear, moisture, and bacteria. However, the joint between the frame and the outer covering creates a crevice which may collect moisture, debris and bacteria. The moisture and bacteria can work deep into the crevice between the frame and the outer membrane where they are sheltered from both detection and removal.
In another attempt to alleviate the existing shortcomings of control panels with membrane switches, the outer covering of the membranes witch is made larger than the remaining layers to overlap and cover the lower layers when the keypad is attached to the control panel. In this manner, the layered edges of the membrane switch are shielded from direct exposure to the elements by the overlapping outer covering. The lower surface of the outer cover is provided with an adhesive which can serve to attach the membrane switch to the control panel and, at the same time, form a protective seal to limit the moisture, debris and bacteria which reach the covered edges of the membrane switch.
However, in this configuration, a bump or discontinuity is created between the edge of the outer layer and the control panel. This bump tends to collect moisture, debris and bacteria. Moreover, in use, objects may catch or snag on the bump causing it to separate from the control panel and allowing moisture and debris to enter under the outer covering. These problems are particularly acute for medical or dental instruments where the control panel is required to be thoroughly scrubbed, often with disinfectants or solvents, on a regular basis. Such scrubbing tends to accelerate separation of the outer covering from the control panel and hasten entry of moisture, debris and bacteria under the membrane switch.